1. Field of the Invention
The present invention relates to a polypeptide having substantially the same antigenicity as that characteristic of a hepatitis B virus and having immunoreactivity with an antibody to the virus. More specifically, the present invention relates to a polypeptide having an amino acid sequence coinciding with a specific portion of an amino acid sequence coded by an X-gene of the hepatitis B virus.
The polypeptide according to the present invention is effective to detect an antibody specific to the hepatitis B virus. The polypeptide according to the present invention can be used as an immunogen dosed to mammals in order to obtain a polyclonal antibody and a monoclonal antibody for an X-protein, i.e., a protein produced by expression of an X-gene.
2. Description of the Related Art
Carriers of a hepatitis B virus (to be referred to as an HBV hereinafter), i.e., people infected by the HBV have reached two billion, and many of them suffer from the chronic hepatitis. It is known that the HBV carriers or patients of the chronic hepatitis will be finally affected by a liver cirrhosis or hepatocellular carcinoma at a high rate.
Since the HBV was found first in serums of native Australians, it was initially called an Australia antibody (JAMA, vol. 191, pp. 541-546 (1965)). Later, the HBV was found to be a 42-nm diameter spherical particle having a double structure, and this particle is called a Dane particle.
The Dane particle has a core having a diameter of 27 nm, and the core is covered with an envelope portion which is a surface antigen called an HBs antigen. The core contains a nucleocapsid or core antigen (HBc antigen and HBe antigen), an incomplete double-chain HBV-DNA having about 3,200 base pairs, and a DNA polmerase necessary for forming this incomplete double-chain.
In recent years, extensive studies have been made on various HBV-associated markers. As one of these studies, it has been confirmed that detection of antigen and antibody characteristic of the hepatitis B is significantly important for clinical diagnosis.
A synthetic polypeptide having an amino acid sequence corresponding to an antigenic portion contained in a perfect HBs antigen is used in an immunoassay system for detecting an HBs antigen and an anti-HBs antibody (Proc. Natl. Acad. Sci. USA, vol. 79, pp. 579-582 (1982)).
The X-protein is a protein having a molecular weight of about 17 kd and coded by an X-gene located on an HBV-genom. The clinical significance of the X-protein has not yet been clarified. Anne Moriarty et al. reported that an antibody against a synthetic protein corresponding to a part of the X-protein is present in hepatocellular caricinoma patients among the HBV carriers at a high rate (Science, vol. 227, pp. 429-433 (1985)). Since then, a relationship between the expression of HBV X-gene and various diseases associated with the hepatitis B virus has received a great deal of attention.